Conventionally, substrate transfer robots have been used for transferring a substrate, such as a semiconductor substrate or a glass substrate. Generally speaking, such a substrate transfer robot includes: a robot arm; a substrate transfer hand attached to the hand end of the robot arm; and a controller. The substrate transfer hand includes a substrate holder for holding a substrate. The substrate can be held by, for example, suction or gripping. Patent Literature 1 describes, as one example, a substrate transfer hand including a plate-shaped blade whose distal end is branched to be Y-shaped. The substrate transfer hand transfers a substrate, with the substrate placed on the blade.
There is a case where the above substrate transfer hand including the Y-shaped blade includes a transmissive optical sensor that is formed by a light emitter and a light receiver. The light emitter is provided on one of the Y-shaped branched distal end portions, and the light receiver is provided on the other distal end portion in a manner to face the light emitter. The presence or absence of a substrate is detected by the transmissive optical sensor. For example, the substrate transfer apparatus described in Patent Literature 1 is configured as follows. The Y-shaped branched distal end portions of the blade are provided with respective sensor supports. A first transmissive optical sensor used for detecting the presence or absence of a substrate and the orientation of the substrate is mounted on the front end side of the sensor supports, and a second transmissive optical sensor used for detecting displacement of the substrate is mounted on the rear end side of the sensor supports.